Transport systems involving a trolley slidable along a suspended length of cable have been known in the art for many years. Commonly known as zip lines, such systems are extensively used for rescue work on ski lift equipment. They are also available as backyard toys for children and adults. Spring Swings, Inc. of Riviera Beach, Fla., manufactures a Fun Ride Deluxe Zip Line kit which can be installed between two trees or other suitable cable supports. The kit includes enough stranded steel aircraft cable for a ride of about 21 meters (70 feet) in length, cable tensioning devices, and a “super tough” double-pulley plastic trolley which travels bidirectionally on the suspended cable. The kit retails for less than $100.
Within the past two decades, zip lines have become part of the “extreme sports” scene. One particular zip line installed on a hill in the Costa Rican jungle has been given rave reviews. The Costa Rican system is really quite primitive, having a trolley with a single deep-groove nylon pulley riding on the suspended cable. In order to slow his descent, a rider must twist the trolley, thereby causing the flanges of the pulley to rub against the cable and generate friction. Kinetic energy is, thus, dissipated as heat. Riders who are particularly heavy may generate so much friction and related heat that the trolley pulley may fail prematurely. Such a system is potentially dangerous, as the riders, themselves, must take responsibility for maintaining their descent speeds within a safe range, in order to avoid smashing into the lower cable support tower. In the absence of a legal system which demands that even the most risk-inclined, incompetent and moronic individuals be protected from themselves, such a zip line system might operate in perpetuity. However, in a country such as the U.S., the slip and fall plaintiffs' bar would kill it almost immediately.
In 2003, a sophisticated, safe, and thoroughly-engineered zip line thrill ride was installed on a steep hill at Park City, Utah. The suspended cable is about 805 meters in length (0.5 mile), and the vertical drop is approximately 183 meters (600 feet). Although maximum speeds in excess of 90 m.p.h. are attainable on the system, the maximum speed experienced by paying riders is automatically limited by the equipment to no more than about 55 m.p.h. Certain components and features of this modern zip line system were the subjects of U.S. Pat. No. 6,666,773 to the same inventor.
The focus of the present invention is a zip line trolley used primarily for downhill thrill rides which are erected as permanent installations and which are often built adjacent ski lifts, in amusement parks, and in other locations with mountainous or hilly terrain frequented by the public.